1. Field of the Invention
The present invention relates to a method and an apparatus for optically picking up an image of an optically readable information code, such as, a barcode or a two-dimensional code.
2. Description of the Related Art
Handheld optical information readers aim at reading an information code, such as a barcode, a two-dimensional code, or another similar code, that is composed of optically readable different colored (such as black-and-white) units (cells, bars, or the like) and is attached to a target, such as a label or a goods, by printing or other similar methods. In this specification, a target itself or a target to which optically readable information is attached is collectively referred to as “target”.
For improving the usability of the handheld optical information readers, a type of handheld optical information readers that can read an information code positioned at a distance therefrom has been provided.
Such type of handheld optical information readers has a handheld body case provided at its one end portion with a reading window, a photodetector, such as a CCD (Charge-Coupled Device) area sensor, an imaging unit with an imaging lens, and a reading unit composed of a light illuminating device. The photodetector, the imaging unit, and the reading unit are installed in the body case, respectively.
In this type optical information reader) a user pushes a trigger switch attached to the handheld body case with the reading window of the handheld body case directed to a target, such as a barcode. The push of the trigger switch causes the light illuminating device to supply light through the reading window toward the target. The light supplied from the light illuminating device is irradiated to the target (barcode) so that light reflected from the target based on the irradiated light enters through the reading window into the imaging unit. The light entered into the imaging unit is focused on the photodetector by the imaging lens to be imaged thereon, so that an image corresponding to the target is picked up by the photodetector.
In this type optical information reader, handling of the optical information reader in user's hand(s) may cause the jiggle of the user's hand(s). In particular, when reading out a target to which an information code is attached at a location far from the information reader, the jiggle of the user's hand(s) with holding information reader may cause noises in the picked-up image; the noises may deteriorate the visibility of the picked-up image.
Regarding ‘jiggle’, in conventional digital cameras including digital video cameras, an image stabilizing function of decreasing the influence of the ‘jiggle’ on the picked-up image has been well known. Thus, it is considered to install such an image stabilizing function in conventional optical information readers.
First example of such a conventional digital camera in which an image stabilizing function is installed is disclosed in Japanese Unexamined Patent Publication No. 2003-57707.
This publication shows a digital camera having a pair of angular rate sensors, a group of correcting lenses, and an electromagnetic actuator. That is, the paired angular rate sensors detect the movement angle of the camera; the electromagnetic actuator makes the correcting lens group move in at least one of horizontal and vertical directions based on the detected movement angle of the camera.
Second example of such a conventional digital camera in which an image stabilizing function is installed is disclosed in Japanese Unexamined Patent Publication No. 2000-298300.
This publication shows an image stabilizing method including the steps of:
picking up an image of an object;
selecting at least two points in the picked-up image;
obtaining a special frequency distribution around each point of the picked-up image to estimate a moving direction thereof;
obtaining an autocorrelation function of adjacent areas of each point of the picked-up image along the moving direction to differentiate the autocorrelation function with respect to the moving direction, thereby estimating the magnitude of the movement of the picked-up image; and
correcting the picked-up image based on the estimated moving direction of the picked-up image and the magnitude of the movement thereof.
In the first example, however, the digital camera is designed so that the electromagnetic actuator mechanically makes the correcting lens group move, which may cause the mechanism of the electromagnetic actuator and the control thereof to increase in complexity, resulting in an increase in cost of the digital camera.
In the second example, however, the image stabilizing method needs the special frequency distribution obtaining step and the autocorrelation function obtaining step, which may cause the image correcting method to increase in complexity and may require considerable time to complete the correction of the picked-up image.